Nuclear Localization of CD26 Induced by a Humanized Monoclonal Antibody Inhibits Tumor Cell Growth by Modulating of POLR2A Transcription

Abstract

CD26 is a type II glycoprotein known as dipeptidyl peptidase IV and has been identified as one of the cell surface markers associated with various types of cancers and a subset of cancer stem cells. Recent studies have suggested that CD26 expression is involved in tumor growth, tumor invasion, and metastasis. The CD26 is shown in an extensive intracellular distribution, ranging from the cell surface to the nucleus. We have previously showed that the humanized anti-CD26 monoclonal antibody (mAb), YS110, exhibits inhibitory effects on various cancers. However, functions of CD26 on cancer cells and molecular mechanisms of impaired tumor growth by YS110 treatment are not well understood. In this study, we demonstrated that the treatment with YS110 induced nuclear translocation of both cell-surface CD26 and YS110 in cancer cells and xenografted tumor. It was shown that the CD26 and YS110 were co-localized in nucleus by immunoelectron microscopic analysis. In response to YS110 treatment, CD26 was translocated into the nucleus via caveolin-dependent endocytosis. It was revealed that the nuclear CD26 interacted with a genomic flanking region of the gene for POLR2A, a subunit of RNA polymerase II, using a chromatin immunoprecipitation assay. This interaction with nuclear CD26 and POLR2A gene consequently led to transcriptional repression of the POLR2A gene, resulting in retarded cell proliferation of cancer cells. Furthermore, the impaired nuclear transport of CD26 by treatment with an endocytosis inhibitor or expressions of deletion mutants of CD26 reversed the POLR2A repression induced by YS110 treatment. These findings reveal that the nuclear CD26 functions in the regulation of gene expression and tumor growth, and provide a novel mechanism of mAb-therapy related to inducible translocation of cell-surface target molecule into the nucleus.

The amino terminus extension in the long dipeptidyl peptidase 9 isoform contains a nuclear localization signal targeting the active peptidase to the nucleus

“…however, in contrast to DPP9, analysis of the DPP8 sequence with the cNLS mapper program does not predict an NLS at the amino terminus of the protein but instead a putative bipartite NLS in all DPP8 isoforms (data not shown). Previously, DPPIV was also reported to localize to the nucleus in human cancer cells such as cultured malignant t cell lines [47,48]. this translocation however is different from that observed for DPP9, and presumably does not involve an NLS, but instead caveolin-dependent endocytosis of DPPIV and a yet not further analyzed mechanism into the nucleus.…”

“…the reduced efficiency of the inhibitor probably leads to an underestimation of the DPP8&9 prolyl peptidase activity in the nucleus. Moreover, in contrast to malignant t cell lines [47,48], Western-blot analysis of heLa nuclear fractions suggests that DPPIV does not contribute to the major DPP activity in this fraction. thus, although we cannot exclude that other unknown enzymes may contribute to prolyl peptidase activity in the nucleus, our results show for the first time the nuclear localization and activity of DPP9 (and DPP8) in this compartment.…”

In-depth Proteomic Analysis of Six Types of Exudative Pleural Effusions for Nonsmall Cell Lung Cancer Biomarker Discovery

“…Similar to sMET, sCD26 originates from the shedding of surface-bound CD26. Overexpression of DPP4 is observed in various human cancers, including thyroid, breast, prostate, and ovarian cancers and is involved in tumor development, invasion, and metastasis (60,61). However, previous studies have also observed that sCD26 was deficient in total homogenates of colon, kidney, lung, and liver tumors (62,63) as well as in different transformed and cancer-derived cell lines (64).…”

Suppression of lung metastases by the CD26/DPP4 inhibitor Vildagliptin in mice

“…Recently, a CD26/DPP4 antibody was employed as a therapeutic measure in mesothelioma and T-cell lymphoma showing down-regulation of RPB1 followed by inhibitory DNA binding of CD26/DPP4 [16][17][18]. In a rat study, the effect of CD26/DPP4-inhibition on colon carcinogenesis was shown by a long term treatment with the CD26/DPP4-inhibitor Sitagliptin [19].…”